In recent years, the fast growing of datacom networks and the large and ever-increasing amount of services made available to the users over such networks, particularly over the Internet, have led to a remarkable growth of traffic which is heavily affecting network performance.
As a matter of fact, current architectures of backbone networks, which were originally designed to support telephone traffic, are inadequate to support huge volumes of Internet data traffic and, ideally, should be replaced by technically advanced, state of the art hardware networks providing sufficient speed and bandwidth to cope with today's and tomorrow's data traffic needs.
Unfortunately, cost is a major issue which is slowing down, if not preventing, the hardware modernisation process: the common feeling is that investments would be too high with respect to expected revenues.
As a consequence, designs of next generations networks (NGNs), although taking into account all critical requirements, are still be based on traditional criteria.
The main requirement for a successful NGN is thus to be seen in the exploitation of the currently available hardware means and available bandwidth thereof, wherein the term bandwidth is to be intended in a broad sense, including data transfer capacity of a communications system, link capacity, node throughput and so on.
Effective use of the available bandwidth can be obtained by means of traffic engineering solutions, which is the possibility of handling network resources in a flexible and dynamic way in order to cope with traffic demand varying with time, optimising the usage of available resources and employing effective routing strategies.
Generally speaking most communications networks are designed on a multi-layer architecture using the well known seven-layer architecture as set out by the Open Systems Interconnection (OSI) and standardised by the International Standards Organization (ISO).
Each of the seven layers provides for a progressive level of abstraction, starting from layer 1, or physical layer, to level 7, the application layer, going through the data link layer, the network layer, the transport layer, the session layer, the presentation layer and the application layer.
Moreover, most of today's networks, including the networks implementing the Internet, use a number of well known and widely available network layer protocols for packet routing and flow control, which is performed at the network layer, and a number of data link layer protocols for error checking or performing functions that make reliable connection between two nodes.
Referring again to a most significant datacom network, the Internet transport infrastructure is progressively migrating towards a model in which an optical core network able to handle high traffic volumes interconnects high throughput routers. In addition, a massive migration of a large part of services is next to occur towards the IP paradigm, including real time and multimedia services and next generation mobile services.
Such a huge amount of data requires appropriate communications means suitable to cope with such high volumes of data traffic, for instance high capacity optical networks exploited through Wavelength Division Multiplexing (WDM) techniques.
Conventionally, routing of packets in an IP based network is performed entirely at the network layer. Upon a data packet arriving at a network node, or router, the network-layer process operating at the node compares a destination address included with the packet to a list of address prefixes stored within a routing table maintained at the node. A longest match prefix is searched for and, upon finding, the packet is forwarded to another node associated with such prefix. The matching process is then repeated at the current node, until the packet destination address is reached.
Of course, several paths may exist in the network leading from a start node to a final destination node. The calculation of an optimal path is a key operation in network engineering and it is the basis for an efficient network performance.
In this context, four layers are typically identified in practice in today's multi-layer data networks: an IP layer for carrying applications and services, an asynchronous transfer mode (ATM) layer for traffic engineering, a SONET/SDH layer for transport and a wavelength-division multiplexing (WDM) layer for capacity.
Unfortunately, such traditional multi-layer architectures suffer from the lowest common denominator effect where one layer can limit the scalability of the entire network and they have proven to be not only also cost ineffective but also hard and slow to scale for very large volumes of traffic.
In fact, since four layers are involved in the actual transport of a packet across the network, calculation of a path, which is carried out in order to optimise performance at a certain layer, is affected by the behaviour in the other three layers.
For these reasons, engineering solutions addressing the issue of using IP over optical networks have therefore been proposed in the state of art, reducing the number of layers to a total of two.
However, even in this shrunk architecture, solutions reported so far either aim at optimising the IP routing process in an Internet network by adopting a proper paradigm, for instance the Multi-Protocol Label Switching (MPLS) one, or to increase the performance of optical networks.
More in detail, MPLS technology has been developed to reduce the amount of time and computational resources used in network routing mechanisms.
MPLS replaces the need to do the longest prefix match at each router by inserting a fixed length label between the network layer header and the link layer header of each data packet. A router can thus easily make a hop decision for an incoming packet merely by using the MPLS label of the packet as an index into a routing table, so decreasing the effort and time required to forward the data packet from a node to another and thus increasing network performance. A detailed description of MPLS is found in E. Rosen et al., Multiprotocol Label Switching Architecture, Internet Draft draft-ietf-mpls-arch-07.txt, Internet Enegineering Task Force (IETF) Network Working Group, January 2001, which is herein incorporated for reference in its entirety.
On the other hand, state of the art the solutions dealing with optical networks refer to the wavelength routing and wavelength assignment problem, usually known as RWA, a problem which may be solved either off-line or on-line.
In the former case, an expected traffic matrix representing the required connections in terms of the number of “wavelengths” that need to be accommodated for each pair of source/destination optical nodes, like optical cross-connects, is used.
In the latter case, the RWA problem is solved dynamically on the basis of requests that arrive with a certain statistic.
Both the IP/MPLS and RWA engineering approaches, however, have not proven to be fully satisfactory, in that optimisation in a layer is still too often affected by critical loads or different situations occurring on the other layer.
Therefore, a need exists in the field for a new strategy relating to a multi-layer network.